Blather. Two disjointed sentences with a couple of common words, but conceptually, nothing that ties them together.

Also, it should be one compound sentence.

The first is content with his life. Happy to sit back and take it in. The second, is more restless. Maybe desperate to prove something.

Or, it’s all nonsense.

Sounds like someone whom I don’t relate to, is failing to make a point about something I don’t care about.

It seems based on assumptions I don’t relate to.

But since you asked, hmm . . . I still don’t know. It might be trying to encourage people to try things, and not worry about what other people think? Or that you don’t have to sit out of activities you might like to try, just because you think you might not be the best at it.

It is borderline gibberish. If it has any meaning for me at all it is a vague impression that people’s opinions of you mean less when you are old.

“If the old man sitting in the bleachers has nothing to prove.”

its maybe because he already completed that stage in his life and can now sit back and watch others complete there health goals.

Then the old man running in a race has nothing to lose.”
Because he is working on his health goals and in the meantime feeling more strength.

Gibberish!
Sounds like an idiot trying to be philosophical.